This invention relates in general to a method and apparatus for centering two concentric cylinders having different diameters.
Pipelines utilized for the transmission of oil and natural gas sometimes require thermal insulation either to retain heat or to keep a liquified product at a reduced temperature. It has been determined in some instances when an insulated pipeline is disposed above ground it is desirable to place the insulated pipe inside of an outer protective jacket which will prevent ultraviolet degradation of the insulation. It is important that the pipe disposed inside of an outer protective jacket be located concentrically with respect to the latter throughout the length of the pipe so as to assure a uniform thickness of insulation.
The sections of pipe, however, typically include an arcuate displacement which tends to bow this pipe at the center. This arcuate displacement can be rather substantial so that the center section of the pipe is significantly off-center even though the outer ends are properly centered with respect to the outer jacket.
In the prior art, the pipe is centered with respect to the outer jacket by means of a mandrel having mechanical crawlers which are rolled inside of the pipe with feelers that provide a read-out of the distance between the pipe and the outer jacket. This centering technique, however, is very time-consuming and extremely inefficient.
The present invention, on the other hand, centers the pipe within the outer jacket by projecting a linear reference line from an illuminating source along the upper, inner surface of the pipe. This reference line is then received at the other end of the pipe by a photo receiver comprising a linear photodiode array. The photo receiver is capable of detecting the amount of arcuate displacement at any point on the pipe by measuring the place at which the reference line strikes the diode array. The arcuate displacement of the pipe causes the reference line to strike the diode array at varying points which are related to the amount of displacement at that point of the pipe. As the pipe is rotated about its center point, displacement readings are periodically taken. Thereafter, the readings are correlated with the points on the pipe where they occurred to indicate the point and amount of maximum arcuate displacement. Once the amount of arcuate displacement has been determined, the outer jacket is displaced a corresponding amount to correct for the bow in the pipe to creat a relatively uniform area between the pipe and the outer jacket.
This centering apparatus and method can also be used to monitor the amount of pipe movement that occurs during the process of filling the cavity between the pipe and the outer jacket with a foamable liquid. This movement is known as floating and occurs when the filling material causes the inner section of pipe to move within the filling cavity. By using the centering apparatus and technique of the present invention, the extent of this movement can be detected so that the outer jacket can be corrected a corresponding amount.
It is therefore, an object of the present invention to provide a method and apparatus for centering two concentric cylinders having different diameters.
Another object of the present invention is to provide a method and apparatus for centering two concentric cylinders having different diameters which is highly accurate and easy to use.
A further object of the present invention is to provide a method and apparatus for centering two concentric cylinders whereby two sections of pipe having different diameters can be positioned with respect to each other to form a uniform filling cavity between them.
A further object of the present invention is to provide a method and apparatus for centering two concentric sections of pipe whereby the amount of floating or movement of the inner section of pipe during the filling operation can be determined so that the outer jacket can be corrected to maintain the uniformity of the filling cavity.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.